Patent Application
20250101558
The present invention relates to a pipe and a manufacturing method therefor, in particular to a high-strength pipe resistant to sodium hydroxide corrosion and a manufacturing method therefor.
As well known in the art, in the current water supply plant site, in order to ensure the water quality, an alkali-washing process of a membrane pool is usually used for treatment. In an actual application process, a dosing pipeline, a flushing pipeline, and a pipeline from the membrane pool to the neutralization pool used in the alkali-washing process of the membrane pool are easily corroded by sodium hydroxide. Therefore, in order to prevent these pipelines from being corroded by sodium hydroxide as much as possible, 304 and 316L stainless steel materials are usually used to manufacture such pipelines.
Under this requirement, the above-mentioned pipelines and devices cannot be manufactured by carbon steel pipes: if carbon steel pipes are used, they will inevitably be corroded by sodium hydroxide, resulting in water pollution, and even pipeline leakage and pipeline bursting.
Compared with carbon steel, the structure of 304 and 316L stainless steel has lower strength. Under the same working conditions, the required thickness is higher, resulting in an increase in the amount of materials used; at the same time, the welding and machining of 304 and 316L stainless steel are more difficult; moreover, 304 and 316L stainless steel themselves contain many noble metal elements such as Cr, Ni, Mo, and the like, resulting in a relatively higher cost of pure stainless steel in the process of production, manufacture, and installation.
Based on above, considering the shortcoming and defect in the application of the above-mentioned 304 and 316L stainless steel and carbon steel in the sodium hydroxide corrosion environment, the present invention expects to obtain a new pipe. The pipe adopts a reasonable design, so it can have a corrosion resistant layer resistant to sodium hydroxide corrosion formed on the surface of the carbon steel base layer, and finally form a pipe having sodium hydroxide-corrosion resistance, good mechanical properties and high economic efficiency, and thus has great economic and social benefits.
One of the purposes of the present invention is to provide a new pipe. The pipe adopts a reasonable design, so it can have a corrosion resistant layer resistant to sodium hydroxide corrosion formed on the surface of the carbon steel base layer, and finally form a pipe having sodium hydroxide-corrosion resistance, good mechanical properties and high economic efficiency.
The pipe according to the present invention can solve the essential deficiency of 304, 316L stainless steel or carbon steel generated under the sodium hydroxide corrosive medium environment in the current water supply plant site, meet continuously increasing requirements for the corrosion resistance and mechanical properties of the pipe of the pipeline devices under the sodium hydroxide medium environment in the water supply plant site, and greatly improve the applicability, safety, and durability of the pipeline devices while avoiding secondary pollution of water quality, and thus has great economic and social benefits.
In order to achieve the above object, the present invention provides a pipe, wherein the pipe has a corrosion-resistant layer and a base layer in its thickness direction, and the corrosion-resistant layer is at least disposed on the inner wall of the pipe, and the corrosion-resistant layer further comprises, in addition to Fe and inevitable impurities, the following chemical elements in percentage by weight:
0<C≤0.05%;
Cr+2.8×Mo+16×N+2×Ti≥22.0%.
Preferably, in the pipe according to the present invention, the corrosion-resistant layer consists of the following chemical elements in weight %:
0<C≤0.05%;
Cr+2.8×Mo+16×N+2×Ti≥22.0%.
In the pipe according to the present invention, in order to ensure the sodium hydroxide corrosion resistance of the pipe, the sodium hydroxide corrosion resistance of the corrosion resistant layer should be ensured at first.
Currently, working conditions of the sodium hydroxide corrosive medium in the existing water supply plant site are: transport medium comprising sodium hydroxide having a mass concentration of 0-30% therein, and the temperature thereof is between 0-40° C.
Based on the above working conditions, the inventors have optimized the chemical element components of the corrosion-resistant layer in the pipe, wherein a certain amount of Ti element is added in particular, and a specialized corrosion-resistant equivalent formula and requirements are designed such that Cr, Mo, N and Ti are controlled to satisfy the formula: Cr+2.8×Mo+16×N+2×Ti≥22.0% so as to further reduce susceptibility to intergranular corrosion, prevent stress corrosion of pipeline device in alkali washing process, and avoid corrosion of weld seam caused by sodium hydroxide solution when the temperature continues to be higher.
In the present invention, the design principle of each chemical element in the corrosion-resistant layer is as follows:
Correspondingly, in the corrosion resistant layer of the pipe according to the present invention, while controlling the mass percentage of a single chemical element alone, the elements Cr, Mo, N and Ti are further controlled to satisfy the formula: Cr+2.8×Mo+16×N+2×Ti≥22.0%. Each element in the formula is substituted into the mass percentage of the corresponding element. Through such control, it can be further ensured that the corrosion-resistant layer has a rather excellent corrosion resistance in the sodium hydroxide environment.
Preferably, in the pipe according to the present invention, in the corrosion resistant layer, the inevitable impurities include: S≤0.030%; P≤0.045%.
In the corrosion resistant layer of the pipe according to the present invention, both P and S are inevitable impurity elements. In order to ensure the quality of the steel, the content of the impurity elements in the steel is preferably as low as possible, if conditions permit.
Preferably, in the pipe according to the present invention, the base layer comprises the following chemical elements in percentage by weight:
N≤0.006%; and
Preferably, in the pipe according to the present invention, the base layer further comprises at least one of the following chemical elements:
0<B≤0.0003%;
0<Ni≤0.20%;
0<Cr≤0.20%;
0<Mo≤0.10%.
In the present invention, in order to ensure that the pipe according to the present invention can obtain higher mechanical properties, the choice of chemical element components of carbon steel in the base layer needs to ensure both high strength and good processability.
Thus, in the present invention, the design principle of each chemical element of carbon steel in the base layer is as follows:
Preferably, in the pipe according to the present invention, in the base layer, the inevitable impurities include: S≤0.010%; P≤0.015%.
In the above technical solution of the present invention, both P and S are inevitable impurity elements in the base layer. S combines with Mn in the steel to form plastic inclusion, i.e., manganese sulfide, which is especially unfavorable to the plasticity and toughness of the steel in transverse direction. Therefore, the content of S element in the base layer should be as low as possible. In addition, P is also a harmful element in steel, which seriously damages the plasticity and toughness of the steel plate.
Therefore, for the present invention, both S and P are inevitable impurity elements, and the content thereof should be as low as possible. Considering the actual steelmaking level of the steel plant, in the base layer according to the present invention, S and P elements may be controlled to satisfy: S≤0.010%; P≤0.015%.
Preferably, in the pipe according to the present invention, the single-layer thickness of the corrosion-resistant layer accounts for 0.5-20% of the total thickness of the pipe, more preferably, the single-layer thickness of the corrosion-resistant layer accounts for 1.2%-16.7% of the total thickness of the pipe. That is to say, if both the inner surface and the outer surface of the pipe have the corrosion resistant layer, each corrosion resistant layer has a thickness accounting for 0.5-20% of the total thickness of the pipe. If only the inner surface of the pipe has a corrosion resistant layer, the corrosion resistant layer has a thickness accounting for 0.5-20% of the total thickness of the pipe.
In the present invention, the thickness of the corrosion-resistant layer is selected depending on the working conditions, which plays a crucial role in obtaining good corrosion resistance, mechanical properties and formability of the pipe according to the present invention. When the corrosion-resistant layer is too thick, it will affect the mechanical properties of the material and production cost; and when the corrosion-resistant layer is too thin, it will reduce the corrosion resistance and service life of the material. Therefore, in the present invention, preferably, the thickness of the single-layer corrosion resistant layer is controlled to account for 0.5-20% of the total thickness of the pipe, and more preferably the single-layer corrosion resistant layer has a thickness accounting for 1.2-16.7% of the total thickness of the pipe.
Preferably, in the pipe according to the present invention, the base layer has a microstructure of ferrite+pearlite, or ferrite+pearlite+bainite; and the corrosion resistant layer has a microstructure of austenite.
Preferably, in the pipe according to the present invention, the pipe has a yield strength of ≥426 MPa, a tensile strength of ≥585 MPa, and an elongation rate of ≥35%, and the corrosion-resistant layer has a uniform corrosion rate (i.e., an average corrosion rate) of ≤0.05 mm/year in an environment with a temperature of ≤40° C. and a sodium hydroxide concentration of ≤30 wt %.
Correspondingly, another object of the present invention is to provide a method for manufacturing the above-mentioned pipe. This method is simple and feasible, and can effectively produce the above-mentioned pipe.
In order to achieve the above object, the present invention provides a method for manufacturing the above-mentioned pipe, wherein the method comprises the steps of:
In the above-mentioned manufacturing method according to the present invention, a high corrosion resistant composite plate (corrosion resistant layer plate+base layer plate) can be obtained by the following method: smelting and casting are designed according to the chemical composition to prepare the corrosion resistant layer slab and the base layer slab, and then the two slabs are assembled. The high corrosion-resistant composite plate obtained is further heated, rolled, and coiled to obtain a hot-rolled coil having a composite interlayer structure. After the hot-rolled coil is subjected to a surface treatment, a pipe-making is performed to obtain the pipeline according to the present invention.
In the present invention, the inventors have optimized the heating and rolling process in step (3) to ensure that a transition layer structure having a certain thickness can be formed between the corrosion resistant layer and the base layer by heating, rolling, and the like, so that the complete metallurgical combination of the corrosion resistant layer and the base layer can be realized, thereby improving the applicability and economy of the material while ensuring the sodium hydroxide corrosion-resistance and mechanical properties.
In the step (2) of the manufacturing method according to the present invention, the corrosion-resistant layer slab and the base slab prepared may be pretreated, and the bonding surface of the slab is sealed by welding all around, and the welded and sealed bonding surface is vacuumized to complete slab assembly.
Correspondingly, in step (5), a surface treatment is carried out on the hot-rolled coil, wherein pickling or mechanical methods can be used to remove phosphorous. In addition, in the process of pipe making of step (6), the conventional methods of spirally welding pipe or longitudinally welding pipe can be used to form and weld. The welding method can be selected from a submerged arc welding, a gas metal arc welding, a tungsten inert gas welding, a plasma arc welding, a shielded metal arc welding, a high-frequency welding or a laser welding.
Preferably, in the manufacturing method according to the present invention, in step (3), the finish rolling temperature is controlled to be 920-1050° C.
Preferably, in the manufacturing method according to the present invention, the method further comprises a preheating step between step (2) and step (3), wherein the preheating temperature is 1150-1230° C.
In the manufacturing method according to the present invention, it is also possible to determine whether or not a preheating process is selected between step (2) and step (3) depending on the performance requirements of the final product. In the preheating process, the composite slab obtained by slab assembly may be heated at a temperature of 1150-1230° C., so that the corrosion resistant layer on the surface of the composite slab can obtain a uniform austenitized structure; such that the carbides that may exist originally is completely dissolved as much as possible, while the compounds of alloying elements such as niobium and titanium in carbon steel are completely or partially dissolved; and such that elements of the corrosion resistance layer and the carbon steel base layer are diffused at the interface to form a stable transition layer, and then slowly cooled to room temperature.
Preferably, in the manufacturing method according to the present invention, the method further comprises a cold rolling and annealing step between step (5) and step (6), preferably, at an annealing temperature of 900-1000° C.
In the manufacturing method of the present invention, in actual use, if the target product before pipe making is a cold-rolled coil other than a hot-rolled coil, the method can further comprise a cold rolling and annealing step between step (5) and step (6). The hot-rolled coil can be cold-rolled to the target thickness, then subject to annealing.
It can be seen from the above that in the present invention, the inventors can finally obtain a plate strip having the sodium hydroxide corrosion resistance, good mechanical properties and high economic efficiency by designing the composition of the corrosion resistant layer and the base layer, designing the compounding ratio of the two, and using a rolling process to form a corrosion-resistant layer resistant to sodium hydroxide on the surface of the carbon steel plate of the base layer, and then process the plate strip into a pipe for pipeline devices used in the environment of sodium hydroxide corrosive medium in water supply plant site.
It should be noted that, in the design process of the present invention, the difficulties include:
In the present invention, by means of reasonable design, the inventors succeeded to overcome the above-mentioned difficulties and obtain the pipe as described in the present invention.
Compared with the prior art, the pipe according to the present invention and the manufacturing method therefor have the following advantages and beneficial effects:
In the present invention, a transitional layer structure having a certain thickness is formed between the corrosion resistant layer and the base layer by means of processes such as heating and rolling and the like, a thus the complete metallurgical bonding of the corrosion resistant layer and the base layer is realized so that the suitability and economy of the materials are improved while ensuring the sodium hydroxide corrosion resistance and mechanical properties.
The pipe manufactured by using the above-mentioned composition design and process control method can solve the essential deficiency of 304, 316L stainless steel or carbon steel generated under the sodium hydroxide corrosive medium environment in the water supply plant site; The pipe can be effectively applied to the pipeline device used in the sodium hydroxide medium environment in the water supply plant site, such as dosing pipeline, flushing pipeline, and pipeline from the membrane pool to the neutralization pool in the alkali-washing process of the membrane pool, and can meet the requirements for the sodium hydroxide corrosion resistance and mechanical properties of the pipelines and the devices, which can greatly improve the applicability, safety, and durability of the pipeline devices while avoiding secondary pollution of water quality, and thus has great economic and social benefits.
Compared with the current 304 and 316L stainless steel pipeline used in the dosing pipeline, the flushing pipeline, and the pipeline from the membrane pool to the neutralization pool and the like in the alkali-washing process of the membrane pool in the water supply plant site, the pipe according to the present invention has high strength, simple welding and mechanical processing, and high economic efficiency. Compared with carbon steel pipe, the steel plate/steel strip of the pipe according to the present invention can dispense with the pipeline corrosion-resistant coating process, and at the same time have the corrosion resistance and durability that are hard for a carbon steel pipe to reach, and are more energy-saving, environment-friendly and maintenance-free.
The pipe and the manufacturing method therefor as described in the present invention will be further explained and described below with reference to specific embodiments/examples, however, the explanation and description do not constitute inappropriate definition to the technical solution of the present invention.
The mass percentages of the chemical elements in the corrosion resistant layers in the pipes of Examples 1-7 are listed in Table 1.
The mass percentages of the chemical elements in the base layers in the pipes of Examples 1-7 are listed in Table 2.
In the present invention, the pipes of Examples 1-7 of the present invention are all manufactured by the following steps:
It should be noted that, in the present invention, the pipes of Examples 1-7 of the present invention are all produced by the process of the above-mentioned step (1)-step (6), and their chemical composition and related process parameters all meet the control requirements of the design specification of the present invention.
The specific process parameters of the pipes of Examples 1-7 in the steps of the above-mentioned manufacturing method are listed in Table 3.
It should be noted that, according to the process parameters shown in the above Table 3, after the surface treatment of the hot-rolled coil in step (5) in Example 1, Example 3 and Example 4, cold rolling and annealing were further carried out, which can correspondingly obtain cold-rolled plates; while hot-rolled plates were obtained by step (5) in Examples 2, 5, 6 and 7 without performing cold rolling and annealing.
Correspondingly, the plates prepared according to the various examples can further prepare corresponding pipes in the process for making the pipe in step (6).
The finished pipes, i.e., the pipes of Examples 1-7 prepared by the above process were sampled, respectively, and the microstructures in the sample pipes of Examples 1-7 were further observed. After observing the microstructures of the pipes of each example, the mechanical properties and sodium hydroxide corrosion resistance of the sample pipelines of Examples 1-7 could be further tested. The obtained test results are listed in the following Table 4.
Relevant performance testing methods are as follows:
Mechanical performance test: was carried out according to GB/T 6396-2008 “Clad steel plates—Mechanical and technological test”, from which the yield strength, tensile strength and elongation of the sample pipes in Examples 1-7 can be obtained.
Sodium hydroxide corrosion resistance test: Each coupon in Example 1-7 was placed in the pipe in the alkali washing process of the membrane pool in the water supply plant (in the environment with a temperature of ≤40° C. and a sodium hydroxide concentration of ≤30 wt %), and taken out to observe the surface condition of the corrosion resistance layer after 3 months and examine the corrosion weight loss to determine whether there was any corrosion phenomenon. The annual corrosion rate of each Example was calculated. Thus, the sodium hydroxide corrosion resistance of the sample pipes in Examples 1-7 can be obtained.
The test results of the microstructure, mechanical properties and sodium hydroxide corrosion resistance of the pipes of Examples 1-7 are listed in Table 4.
It can be seen from the above Table 4 that in the present invention, the pipes of Examples 1-7 have the yield strength between 426-507 MPa, the tensile strength between 585-650 MPa, and the elongation rate between 35.8-40.0%, and the annual corrosion rate of sodium hydroxide in the test environment is ≤0.04 mm/year.
It can be seen from the above examples that the present invention can obtain a pipe having good corrosion resistance and mechanical properties through appropriate material selection, composition design, rolling and heat treatment processes in combination with the pipe-making process. The pipe in the present invention can solve the essential deficiency of 316L stainless steel or carbon steel generated under sodium hydroxide corrosive medium environment in the current water supply plant site, and meet continuously increasing requirements for the corrosion resistance and mechanical properties of the pipe of the pipeline devices used in the sodium hydroxide medium environment in the water supply plant site, and thus has great economic and social benefits.
As shown in
As shown in
As shown in
It can be found by observation that in Example 3, the microstructure of the base layer in the pipe is ferrite+pearlite+bainite; the microstructure of the corrosion-resistant layer is austenite; correspondingly, in the present invention, the elements of the corrosion-resistant layer and the base layer diffuse at the bonding interface to form a stable transition layer, and the diffusion distance is about 50 μm.
It should be noted that that the prior art portions in the protection scope of the present disclosure are not limited to the examples set forth in the present application file. All the prior art contents not contradictory to the technical solution of the present invention, including but not limited to prior patent literature, prior publications, prior public uses and the like, may all be incorporated into the protection scope of the present invention.
In addition, the ways in which the various technical features of the present invention are combined are not limited to the ways recited in the claims of the present invention or the ways described in the specific examples. All the technical features recited in the present invention may be combined or integrated freely in any manner, unless contradictions are resulted.
It should also be noted that the Examples set forth above are only specific examples of the present invention. Obviously, the present invention is not limited to the above Examples. Similar variations or modifications made thereto can be directly derived or easily contemplated from the contents disclosed by the present invention by those skilled in the art. They all fall within the protection scope of the present invention.
| Number | Date | Country | Kind |
|---|---|---|---|
| 202210084010.2 | Jan 2022 | CN | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/CN2023/072769 | 1/18/2023 | WO |
